Process for producing niobium and tantalum compounds

ABSTRACT

A process for producing valve metal oxides, such as tantalum pentoxide or niobium pentoxide with a narrow particle size distribution within a desired particle size range, is provided. According to the process of the present invention, the valve metal fraction from digestion of valve metal material containing ore is processed under controlled temperature, pH, and residence time conditions to produce the valve metal pentoxide and pentoxide hydrates. Also, disclosed are new tantalum pentoxide and niobium pentoxide products and new tantalum pentoxide precursors and niobium pentoxide precursors.

FIELD OF THE INVENTION

The present invention relates to an improved process for producing valvemetal compounds, such as niobium (columbium) compounds including niobiumoxides and niobium hydrates, and tantalum compounds including tantalumoxides and tantalum hydrates. The present invention also relates tonovel valve metal compounds, in particular to novel niobium oxides,niobium hydrates, tantalum oxides and tantalum hydrates.

BACKGROUND OF THE INVENTION

The term “valve metal” refers to metals such as vanadium, tantalum andniobium that are often utilized in valves, such as the intake/exhaustvalves in engines. A commercially valuable form of a valve metal is avalve metal oxide such as a tantalum pentoxide, (Ta₂O₅) or a niobiumpentoxide (Nb₂O₅) which are produced from mineral ores.

Minerals of concentrates containing tantalum and niobium areconventionally extracted with hydrofluoric acid (HF) or mixtures ofhydrofluoric acid and sulfuric acid (HF/H₂SO₄). The tantalum and niobiumheptafluoro complexes formed are typically separated by solventextraction.

In a conventional process for producing tantalum pentoxide (Ta₂O₅), thetantalum fraction from the ore and solvent extraction is stripped intothe aqueous phase, and tantalum pentoxide is precipitated using ammoniaand recovered by filtration. Niobium pentoxide may be produced in asimilar fashion.

Typical conventional processes for producing niobium pentoxides/hydratesand tantalum pentoxides/hydrates are batch processes Disadvantagesinherent with batch processes include the need to clean and reloadprocessing vessels, that batch size is limited to the size of theprocessing equipment, and that the production of large quantities ofmaterial requires multiple batch runs.

In addition, in conventional processes for producing tantalumpentoxides/hydrates and niobium pentoxides/hydrates it is difficult tocontrol the particle size, and the particle size distribution of thepentoxides and hydrates produced.

For many applications, it is desirable to have a tantalum pentoxide, orniobium pentoxide, product with a consistent particle size (i.e. anarrow particle size distribution). In addition, for many applicationsit is desirable to have a tantalum pentoxide, or niobium pentoxide,having large dense spherical particles (a particle size greater than orequal to 5 micrometers (μm)) and a bulk density of 2.0 g/cc or greaterfor Ta₂O₅ and 1.2 g/cc or greater for Nb₂O₅. For other applications lowbulk density fine particle sizes are preferred (a particle size lessthan or equal to 5 μm) and a bulk density of less than 2.0 for Ta₂O₅ andless than 1.2 for Nb₂O₅. The present invention advantageously allows theproduction of tantalum pentoxide, or niobium pentoxide, products withnarrow particle size distributions within a desired particle size range.

SUMMARY OF THE INVENTION

The present invention provides a process for producing valve metalpentoxides, such as tantalum pentoxide or niobium pentoxide, with anarrow particle size distribution within a desired particle size range.

According to the present invention a process for producing valve metalpentoxides comprises:

-   -   reacting an aqueous solution comprising a valve metal compound        with a base solution under controlled temperature, pH and        residence time conditions to precipitate valve metal pentoxide        precursor;    -   converting the valve metal pentoxide precursor to valve metal        pentoxide; and    -   separating and recovering the valve metal pentoxide. Among the        valve metal compounds suitable for use in the process of the        present invention are included the valve-metal compounds found        in naturally occurring ores and valve metal compounds produced        as products or by-products in industrial processes.

In a preferred embodiment of the process of the present invention, theaqueous solution comprises a valve-metal fluoro compound such as thoseformed during digestion of naturally occuring tantalum and niobiumcontaining ores. The aqueous solution in this preferred embodiment ofthe present invention will be an aqueous-flouro solution. According tothe process of the present invention a valve metal-fluoro compoundmaterial is processed under controlled temperature, pH and residencetime conditions to produce the valve metal pentoxide. In particular,according to the present invention, a process for producing a valvemetal pentoxide comprises:

-   -   reacting an aqueous fluoro-solution comprising a valve        metal-fluoro compound with an ammonia containing solution under        controlled temperature, pH and residence time conditions to        precipitate valve metal pentoxide precursor;    -   converting the valve metal pentoxide precursor to valve metal        pentoxide; and    -   separating and recovering the valve metal pentoxide.

Further details relating to the process of the present invention are setforth below in the Detailed Description of the Invention Section.

The present invention also provides new valve metal pentoxide products,in particular new niobium pentoxide products and new tantalum pentoxideproducts.

A first embodiment of calcined niobium pentoxide powders of the presentinvention may be characterized by having a BET surface area of less thanor equal to 6 square meters per gram (m²/g), preferably less than orequal to 3 m²/g, more preferably less than or equal to 0.5 m²/g; and apacked bulk density of greater than 1.8 grams per cubic centimeter(g/cc), preferably greater than or equal to 2.1 g/cc. The firstembodiment of calcined niobium pentoxide powders may be furthercharacterized as comprising substantially spherical particles.

A second embodiment of calcined niobium pentoxide powders of the presentinvention may be characterized by having a BET surface area of greaterthan or equal to 2 m²/g, preferably greater than or equal to 4 m²/g,more preferably greater than or equal to 6 m²/g; and a packed bulkdensity of less than or equal to 1.8 g/cc, preferably less than or equalto 1.0 g/cc, more preferably less than or equal to 0.75 g/cc.

A first embodiment of calcined tantalum pentoxide powders of the presentinvention may be characterized by having a BET surface area of less thanor equal to 3 m²/g, preferably less than or equal to 0.75 m²/g, morepreferably less than or equal to 0.4 m²/g; and a packed bulk density ofgreater than 3.0 g/cc, preferably greater than or equal to 3.8 g/cc,more preferably greater than or equal to 4.0 g/cc. The first embodimentof calcined tantalum pentoxide powders may be further characterized ascomprising substantially spherical particles.

A second embodiment of calcined tantalum pentoxide powders of thepresent invention may be characterized by having a BET surface area ofgreater than or equal to 3 m²/g, preferably greater than or equal to 7m²/g, more preferably greater than or equal to 11 m²/g; and a packedbulk density of less than or equal to 3.0, preferably less than or equalto 1.1 g/cc, more preferably less than or equal to 0.75 g/cc.

Further details relating to the products of the present invention arealso set forth in the following Detailed Description of the Inventionsection.

In addition, the present invention provides new valve metal pentoxideprecursors, in particular new niobium pentoxide precursors and newtantalum pentoxide precursors. The valve metal pentoxide precursors ofthe present invention may be processed to produce advantageous valvemetal pentoxide products.

The valve metal pentoxide precursors of the present invention arecharacterized by having a line broadened d-value under x-ray analysisat:

-   -   6±0.3;    -   3±0.2; and    -   1.8±0.1.

A first embodiment of niobium pentoxide precursors of the presentinvention may be further characterized by having a BET surface area ofless than or equal to 3 m²/g, preferably less than or equal to 0.5 m²/g;and a Fluoride content of less than or equal to 500 parts per million(ppm), preferably less than or equal to 150 ppm.

A second embodiment of niobium pentoxide precursors of the presentinvention may be further characterized by having a BET surface area ofgreater than 3 m²/g, preferably greater than or equal to 50 m²/g; and aFluoride content of less than or equal to 500 ppm, preferably less thanor equal to 150 ppm.

A first embodiment of tantalum pentoxide precursors of the presentinvention may be further characterized by having a BET surface area ofless than or equal to 3 m²/g, preferably less than or equal to 0.4 m²/g;and a Fluoride content of less than or equal to 500 ppm, preferably lessthan or equal to 150 ppm.

A second embodiment of tantalum pentoxide precursors of the presentinvention may be further characterized by having a BET surface area ofgreater than 3 m²/g, preferably greater than or equal to 17 m²/g; and aFluoride content of less than or equal to 500 ppm, preferably less thanor equal to 150 ppm.

The valve metal pentoxide precursors of the present invention aredescribed in more detail in the following Detailed Description of theInvention section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a possible reactor system for carrying out a preferredprocess of the present invention.

FIGS. 2 a, 2 b, 2 c and 2 d are scanning electron microscope (SEM)photographs of a calcined niobium pentoxide powder of the presentinvention produced in the manner described in Example 3 below. FIG. 2 awas produced at 100 times magnification, FIG. 2 b at 500 timesmagnification, FIG. 2 c at 1000 times magnification and FIG. 2 d at10,000 times magnification.

FIGS. 3 a, 3 b, 3 c and 3 d are SEM photographs of a calcined niobiumpentoxide powder of the present invention produced in the mannerdescribed in Example 5 below. FIG. 3 a was produced at 100 timesmagnification, FIG. 3 b at 500 times magnification; FIG. 3 c at 1000times magnification and FIG. 3 d at 10,000 times magnification.

FIGS. 4 a, 4 b, 4 c and 4 d are SEM photographs of a calcined tantalumpentoxide powder of the present invention produced in the mannerdescribed in Example 9 below. FIG. 4 a was produced at 100 timesmagnification, FIG. 4 b at 500 times magnification, FIG. 4 c at 1000times magnification and FIG. 4 d at 5,000 times magnification.

FIGS. 5 a, 5 b, 5 c and 5 d are SEM photographs of a calcined tantalumpentoxide powder of the present invention produced in the mannerdescribed in Example 10 below. FIG. 5 a was produced at 100 timesmagnification, FIG. 5 b at 500 times magnification, FIG. 5 c at 1000times magnification and FIG. 5 d at 5,000 times magnification.

FIG. 6 is a graph of Zeta potential as a function of pH for tantalumhydroxide filtercake suspensions, at various concentrations of NH₄F.

FIG. 7 is an example of a graph of x-ray d-value for a valve metalpentoxide precursor of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As set forth above, the present invention provides a process forproducing valve metal oxides, such as tantalum pentoxide or niobiumpentoxide. The process of the present invention may be advantageouslyutilized to produce valve metal pentoxides with a narrow particle sizedistribution within a desired particle size range and with low residualfluoride content.

As set forth above, in heretofore utilized processes for producingtantalum pentoxides/hydrates and niobium pentoxides/hydrates it has beendifficult to control the particle size and the particle sizedistribution of the pentoxides and hydrates produced. While not wishingto be bound by any theory, this difficulty is believed to result, inpart, because in a conventional process, tantalum pentoxide particles,or niobium pentoxide particles, are precipitated over a range of pH's.In conventional processes, tantalum pentoxide, or niobium pentoxide, isprecipitated from an aqueous solution through the addition of ammonia tothe solution. The addition of ammonia raises the pH of the solution,however the rise in pH occurs over time as the ammonia reacts with thesolution. It is believed that the precipitation of tantalum pentoxide,or niobium pentoxide, begins at a first pH and continues as the pHcontinues to rise, and ends at a pH higher than the first pH The pH atwhich precipitation occurs affects the particle size of theprecipitates, and thus it is believed that as precipitation occurs overa range of pH's, different particle size precipitates (tantalumpentoxides or niobium pentoxides) are produced, thereby increasing theparticle size distribution. The precipitation over a wide range of pHalso makes it difficult to produce tantalum pentoxides, or niobiumpentoxides, of a particular particle size, particularly in a batchprocess.

We have discovered that this problem, and other disadvantages of theprior art processes, may be overcome by the process of the presentinvention. According to the process of the present invention, thesolvent extracted valve metal fraction from digestion of valve metalcontaining ore is processed under controlled temperature, pH andresidence time conditions to produce the valve metal pentoxide. Moreparticularly, according to a preferred embodiment of the presentinvention, a process for producing a valve metal pentoxide comprises:

-   -   reacting an aqueous fluoro-solution comprising a valve        metal-fluoro compound with an ammonia containing solution under        controlled temperature, pH and residence time conditions to        precipitate valve metal pentoxide precursor; and    -   converting the valve metal pentoxide precursor to valve metal        pentoxide; and    -   separating and recovering the valve metal pentoxide.

With reference to the valve metal tantalum, a process for producingtantalum pentoxide comprises:

-   -   reacting an aqueous fluoro-solution comprising a tantalum-fluoro        compound with an ammonia containing solution under controlled        temperature, pH and residence time conditions to precipitate        tantalum pentoxide precursor; and    -   converting the tantalum pentoxide precursor to tantalum        pentoxide; and    -   separating and recovering the tantalum pentoxide.        Product purity may be controlled by the purity of the valve        metal fraction fed into the system. Complexing agents, such as        EDTA (ethylenediaminetetraacetic acid) and the like, may be        added to the aqueous fluoro-solution to aid in retaining        impurities in solution.

Similarly, according to the present invention, a process for producingniobium pentoxide comprises:

-   -   reacting an aqueous fluoro-solution comprising a niobium-fluoro        compound with an ammonia containing solution under controlled        temperature, pH and residence time conditions to precipitate        niobium pentoxide precursor; and    -   converting the niobium pentoxide precursor to niobium pentoxide;        and    -   separating and recovering the niobium pentoxide.        Product purity may controlled by the purity of the valve metal        fraction fed into the system. Complexing agents, such as those        listed above may be added to the aqueous fluoro-solution to aid        in retaining impurities in solution.

As used herein, an aqueous fluoro-solution is a solution which includesfluorine ions.

A preferred method for controlling the reaction temperature, pH, andresidence time is through the use of a cascading draft tube reactorsystem wherein the reaction between the valve metal fluoro compound,e.g., a tantalum-fluoro compound or niobium-fluoro compound, and theammonia is begun in a first reaction vessel at a first pH andtemperature, and then continues through one or more additional reactionvessels which may be maintained at different pH's and/or differenttemperatures. Thus, according to a preferred method of the presentinvention, a process for producing a valve metal pentoxide comprises:

-   -   introducing an aqueous fluoro-solution comprising a valve        metal-fluoro compound into a first vessel maintained at a first        temperature;    -   introducing a first ammonia solution into the first vessel and        mixing the first ammonia solution and the aqueous        fluoro-solution to obtain a first mixture at a first pH to react        the first ammonia solution and the aqueous fluoro-solution and        initiate precipitation of valve metal pentoxide precursor;    -   transferring said first mixture into a second vessel maintained        at a second temperature and a second pH to produce a second        mixture and mixing to continue precipitation of valve metal        pentoxide precursor;    -   converting the valve metal pentoxide precursor to valve metal        pentoxide; and    -   separating and recovering the valve metal pentoxide.        In the process of the present invention the first pH (in the        first vessel) and the second pH (in the second vessel) may be        substantially the same or different, and may be controlled        independently. If desired, the second pH may be controlled by        the step of introducing a second ammonia solution into the        second vessel and mixing the second ammonia solution and the        first mixture to react the first mixture and the second ammonia        solution obtain the second mixture at the second pH.

A process for producing tantalum pentoxide comprises:

-   -   introducing an aqueous fluoro-solution comprising a        tantalum-fluoro compound into a first vessel maintained at a        first temperature;    -   introducing a first ammonia solution into the first vessel and        mixing the first ammonia solution and the aqueous        fluoro-solution to obtain a first mixture at a first pH and to        react the first ammonia solution and the aqueous fluoro-solution        and initiate precipitation of tantalum pentoxide precursor;    -   transferring said first mixture into a second vessel maintained        at a second temperature and a second pH to produce a second        mixture and mixing to continue precipitation of tantalum        pentoxide precursor;    -   converting the tantalum pentoxide precursor to tantalum        pentoxide; and    -   separating and recovering the tantalum pentoxide.        More preferably, the process includes the additional step of        transferring said second mixture into a third vessel maintained        at a third temperature and further mixing the second mixture to        complete precipitation of tantalum pentoxide precursor prior to        converting the tantalum pentoxide precursor to tantalum        pentoxide. Where it is desired to further control the second pH,        the process may also include the additional step of introducing        a second ammonia solution into the second vessel and mixing the        second ammonia solution and the first mixture to obtain the        second mixture at the second pH and to react the first mixture        and the second ammonia solution to continue precipitation of        tantalum pentoxide precursor.

Similarly, a preferred method for producing niobium pentoxide comprises:

-   -   introducing an aqueous fluoro-solution comprising a        niobium-fluoro compound into a first vessel maintained at a        first temperature;    -   introducing a first ammonia solution into the first vessel and        mixing the first ammonia solution and the aqueous        fluoro-solution to obtain a first mixture at a first pH and to        react the first ammonia solution and the aqueous fluoro-solution        and initiate precipitation of niobium pentoxide precursor;    -   transferring said first mixture into a second vessel maintained        at a second temperature and a second pH to produce a second        mixture and mixing to continue precipitation of niobium        pentoxide precursor;    -   converting niobium pentoxide precursor to niobium pentoxide; and    -   separating and recovering the niobium pentoxide.        More preferably, the process includes the additional step of        transferring said second mixture into a third vessel maintained        at a third temperature and further mixing the second mixture to        complete precipitation of niobium pentoxide precursor prior to        converting the niobium pentoxide precursor to niobium pentoxide.        Where it is desired to further control the second pH, the        process may also include the additional step of introducing a        second ammonia solution into the second vessel and mixing the        second ammonia solution and the first mixture to obtain the        second mixture at the second pH and to react the first mixture        and the second ammonia solution to continue precipitation of        niobium pentoxide precursor.

Although in each of the foregoing descriptions, introduction of theaqueous fluoro-solution is listed before introduction of the ammoniasolution into the first vessel, either solution may be introduced firstinto the vessel. In addition, although a first and a second reactionvessel have been described in each description, additional reactionvessels may be utilized to further control the process. For example, tworeaction vessels, maintained at slightly different pH's could besubstituted for the first and/or the second vessel, thereby raising thetotal number of reaction vessels to four or five.

The valve-metal pentoxide precursor will generally comprise avalve-metal pentoxide hydrate. Conversion from valve-metal pentoxideprecursor to valve metal pentoxide may be accomplished by calcining orby a hydrothermal process. Tantalum-oxide precursors may be converted totantalum pentoxide by calcining at temperatures greater than, or equalto, 790° C. Niobium-oxide precursors may be converted to niobiumpentoxide by calcining at temperatures greater than, or equal to, 650°C.

The residence time for the reactions in each vessel may be controlled bycontrolling the rate at which solutions are introduced into andtransferred from the vessel. Control of the residence time impactsparticle size and density. Increased residence time increases particlesize and density. Temperature can also impact particle size, highertemperatures tend to speed precipitation reaction and generate finerparticles.

In the preferred methods of the present invention, controlling the pHand temperature of each vessel allows the production of valve metalpentoxides (e.g, tantalum or niobium pentoxides), having desiredparticle sizes and narrow particle size distributions to be produced. Inthe process of the present invention pH may be controlled by controllingthe addition of ammonia. The first pH (the pH in the first vessel)should be maintained at a level sufficient to initiate precipitation ofthe tantalum or niobium pentoxide product. Generally the first pH shouldrange from 6 to 9.5, preferably from 7 to 8 for agglomerated particles.The second pH (the pH in the second vessel) should most preferably bemaintained at a level sufficient to assure substantially completeprecipitation of the tantalum or niobium pentoxide precursor. Generallythe second pH should range from 8 to 9.5, preferably from 8 to 8.5. Whenthe first pH in the first reaction vessel is towards the acidic side,addition of the second ammonia solution in the second vessel may benecessary to achieve the desired second pH. In a preferred three vesselembodiment of the process of the present invention, no additionalammonia is added in the third vessel, and the pH of the third vesselwill be substantially the same as, or slightly less than, the pH in thesecond vessel thus assuring that the precipitation reactions proceed tosubstantial completion.

The choice of pH for each vessel will determine, in part, the particlesize of the pentoxide product produced by the process. In general, theextremes of pH, i.e. near 6 and 9.5, in the first vessel areadvantageous for producing fine particle sizes, with pH's in the middleof the range, i.e. near 7.5 advantageous for producing substantiallyspherical (coarse) particle sizes.

As used herein, residence time refers to the time period in which areaction or reactions is/are occurring. Total or overall residence timefor the process is the sum of the residence time in each reactionvessel. The minimum residence time for the process is a residence timesufficient to precipitate a valve metal pentoxide precursor. The maximumresidence time for the process will generally be dictated by the desiredproduct and the economics of the process. In general, for given pH's andtemperatures, shorter total residence times are desirable for producingfine particle size and longer total residence times are desirable forproducing coarse substantially spherical particle sizes. It is alsoadvantageous for the total residence time to be the shortest time for agiven temperature and pH(s) which allows substantially completeconversion of the valve metal-fluoro compound to the desired valve metalpentoxide precursor. As will be understood by those of ordinary skill inthe art, longer residence times may be achieved by recycling of thesolids phase.

The temperature of the reaction vessels may be controlled byconventional means including water jackets and the like. Generally, forlarge scale production, the temperature of each vessel will range from40° C. to 95° C. For given pH's and residence times, higher temperatureswill produce finer particles and lower temperatures will produce coarserparticles.

The relationship between pH, temperature and residence time, may begenerally summarized as follows: Particle Total Residence Size TimeTemperature First pH Second pH Fine Shorter Higher >8 or <7 8-9.5 CoarseLonger Lower 7-8 8-9.5This table is provided by way of illustration only, and is not meant,nor should be construed, to limit the scope of the process of thepresent invention.

An advantage of the process of the present invention is that the processmay be utilized to produce valve metal pentoxide products of a desiredparticle size with a narrow particle size distribution.

Another advantage of the process of the present invention is that theprocess may be performed in a continuous manner, thereby providing acontinuous process for producing valve metal pentoxides, such astantalum pentoxide or niobium pentoxide, with a narrow particle sizedistribution within a desired particle size range.

A further advantage of the process of the present invention is that theprocess may be utilized to produce valve metal pentoxide products of acoarse substantially spherical particle size with high bulk density orfine particles of low bulk density.

A further advantage of the process of the present invention is that theprocess may be utilized to produce a wide range of high purity valvemetal pentoxide products. Operating at elevated temperatures shifts thefollowing reactions to the right, thus promoting completion of thefollowing reactions to product:H₂TaF₇+7NH₄OH=>Ta(OH)₅+7NH₄F+2H₂OH₂NbOF₅+5NH₄OH=>Nb(OH)₅+5NH₄F+H₂O.

Further details relating to the process of the present invention willbecome apparent to those of ordinary skill in the art from the followingdiscussion of a preferred embodiment of the present invention depictedin FIG. 1, which is a process for producing niobium pentoxide products.

With reference to FIG. 1, a cascading draft tube reactor system suitablefor carrying out a preferred embodiment of the present inventioncomprises a series of reaction vessels, with draft tubes, andcirculation means (stirring means), all shown in cross-sectional view inFIG. 1. Reaction vessels, draft tubes, and circulation means suitablefor use in the process of the present invention are commercially known,and therefore are not described in detail herein. Moreover, the processof the present invention is not limited to being performed by particularequipment, and may be performed by a wide variety of different equipmentsuitable for carrying out the process steps described above and below.

In a preferred process of the present invention, the niobium containingfraction 2 from digestion and separation of a niobium containing ore isadded to the top center of a first reaction vessel 10. The rate ofaddition of the niobium containing fraction 2 will depend on the size ofthe reaction vessel, the desired residence time for the reactionsoccurring in the vessel, and the rate at which the first mixture istransferred out of the vessel. This can be any level, e.g., dependingupon the type of particles desired.

An ammonia solution 4 is added to the bottom outer periphery of thefirst reaction vessel 10 outside the area defined by draft tube 12. Therate of addition of the ammonia solution 4 will also depend on the sizeof the reaction vessel, the desired residence time for the reactionsoccurring in the vessel, and the rate at which the first mixture istransferred out of the vessel. In addition, the rate of addition of theammonia solution 4 will depend on the desired pH of the first mixture,pH₁. The pH of the first mixture, pH₁, is determined, in part, by theparticle size desired in the final product. Generally, pH₁ ranges from 6to 9.5. For a given temperature and residence time, pH₁ values near theextremes of the range (near 6 or 9) will produce a finer particle sizein the final product while pH₁ values near the center of the range(between 7 and 8) will produce a coarse spherical particle size in thefinal product.

The first reaction vessel 10 is maintained at a first temperature, T₁.The temperature T₁ of the first vessel is determined, in part, by theparticle size desired in the final product. Generally, T₁ ranges from 30to 95° C., and preferably from 50 to 70° C. For a given pH and residencetime, higher values for T₁ will result in final product having finerparticle sizes. A water jacket (not shown in FIG. 1), or other meansknown to the art, may be utilized to maintain the first reaction vessela T₁.

Circulation means 14 are utilized to circulate and mix the niobiumcontaining fraction 2 and the ammonia solution 4 within reaction vessel10 to create a first mixture. The direction of flow of the first mixturewithin the first reaction vessel may be as shown by the arrows.

During circulation, a portion of the first mixture will exit the firstreaction vessel through pipe 16. The residence time for the reactionsoccurring in the first mixture may be controlled by varying thethroughput rate, and/or the height and size of the reactor. Theresidence time of the first mixture in the first reaction vessel, R₁,will determine, in part, the density of the final product. Thus, byvarying R₁ different density products may be produced. Generally R₁ willrange from 0.03 hours (1.8 minutes) to 2.0 hours (120 minutes), andpreferably from 0.2 hours (12 minutes) to 1.5 hours (90 minutes). For agiven pH₁ and T₁, higher values for R₁ will result in a final producthaving packed bulk densities of 1.2 g/cc or more.

The portion of the first mixture that exits the first reaction vessel 10through pipe 16 is introduced into the inner periphery of a secondreaction vessel 20 inside the area defined by draft tube 22. The rate ofaddition of the first mixture into the second reaction vessel 20 willdepend on the rate at which the first mixture is transferred out of thefirst reaction vessel 10.

An ammonia solution 6 is added to the outer periphery and near thebottom of the second reaction vessel 20 outside the area defined bydraft tube 22. The rate of addition of the ammonia solution 6 willdepend upon the size of the second reaction vessel, the desiredresidence time for the reactions occurring in the second reactionvessel, and the rate at which the first mixture is transferred into thesecond reaction vessel. In addition, the rate of addition of the ammoniasolution 6 will depend on the desired pH of the second mixture, pH₂. ThepH of the second mixture, pH₂, is determined, in part, by the particlesize desired in the final product. Generally, pH₂ ranges from 8 to 9.5,depending upon the pH of the first reactor. For a given temperature andresidence time, pH₂ values are selected to assure complete reactionwhile limiting the amount of ammonia consumed.

The second reaction vessel 20 is maintained at a second temperature, T₂.The temperature T₂ of the second vessel is determined, in part, by thedensity of particles desired in the final product and the rate ofreaction. Generally, T₂ ranges from 30 to 95° C., preferably 60 to 85°C. For a given pH and residence time, higher values for T₂ will resultin final product with a finer particle size. A water jacket (not shownin FIG. 1), or other means known to the art, may be utilized to maintainthe second reaction vessel at T₂.

Circulation means 24 are utilized to circulate and mix the first mixtureentering the second reaction vessel and the ammonia solution 6 withinreaction vessel 10 to create a second mixture. The direction of flow ofthe second mixture within the second reaction vessel is shown by thearrows. Reversal of flow can effect particle characteristics dependingon desired products.

During circulation, a portion of the second mixture will exit the secondreaction vessel through pipe 26. The residence time for the reactionsoccurring in the second mixture may be controlled by varying thecirculation rate and the height and size of the reactor. The residencetime and temperature of the second mixture in the second reactionvessel, R₂, will determine, in part, the completion of reaction withinthe second vessel. To some degree it allows further precipitating anddensification of the particles. Thus, by varying R₂, different particlesize products may be produced. Generally R₂ will range from 0.03 hr (1.8minutes) to 1.5 hr (90 minutes), preferably from 0.05 hour (3 minutes)to 0.8 hour (48 minutes). For a given pH₂ and T₂, higher values for R₂will result in final product having denser and coarser particles.

The portion of the second mixture that exits the second reaction vessel20 through pipe 26 is introduced into the inner periphery of a thirdreaction vessel 30 inside the area defined by draft tube 32. The rate ofaddition of the second mixture into the third reaction vessel 30 willdepend on the rate at which the second mixture is transferred out of thesecond reaction vessel 20.

Circulation means 34 are utilized to circulate and continue mixing ofthe second mixture in the third reaction vessel to allow theprecipitation of niobium pentoxide to proceed to substantial completion.The direction of flow of the second mixture within the third reactionvessel is shown by the arrows but is not a limiting characteristic ofthe reaction. Because no additional ammonia is added to the thirdreaction vessel, the pH of the mixture in the third reaction vessel,pH₃, will be slightly less than pH₂ depending upon the degree ofreaction completion in the third reaction vessel along with ammoniavolatilization rates.

The third reaction vessel 30 is maintained at a third temperature, T₃.The temperature T₃ of the third vessel is determined, in part, by thedegree of reaction completion desired in the vessel. Generally, T₃ranges from 40 to 95° C., preferably 60 to 85° C. For a given pH andresidence time, higher values for T₃ will result in final productreaction being essentially complete. A water jacket (not shown in FIG.1), or other means known to the art, may be utilized to maintain thethird reaction vessel at T₃.

During circulation, a portion of the mixture will exit the thirdreaction vessel through an exit pipe 36. The residence time for thereactions occurring in the third reaction vessel may be controlled byvarying the circulation rate and size of the reaction vessel.

The residence time of the mixture in the third reaction vessel, R₃, willdetermine, in part, the completion of reaction to the final product.Thus, by varying R₃, different degrees of reaction may be produced.Generally R₃ will range from 0.03 hr (1.8 minutes) to 1.5 hr (90minutes), preferably from 0.05 hr (3 minutes) to 0.8 hr (48 minutes).For a given pH₃ and T₃, higher values for R₃ will result in finalproduct having denser particles.

The solution exiting the third reaction vessel 30 through exit pipe 36travels to conventional processing equipment wherein the precipitatedniobium pentoxide solids are recovered from the solution byliquid/solids separation step 40. The liquid/solids separation step maybe performed in any manner known to the art, such as by filtering.Preferably the liquid/solids separation step is performed by a vacuum orpressure filter.

As will be understood by those of ordinary skill in the art, the overallresidence time, or the residence time in a reaction vessel may beincreased by recycling all, or a portion, of the solution and/or solidsexiting each vessel. In particular, an effective way of increasingoverall residence time would be to recycle all or a portion of theprecipitated solids formed by the process back into the initial vessel.Where recycling is utilized, the effective residence times in eachvessel, and/or the effective overall residence time, may be greater thanthose set forth above for at least a portion of the reacting solution.

After separation of the niobium pentoxide solids, the solids which arenot recycled may be washed as shown by solids washing step 50. Solidswashing may be accomplished in manners conventional in the art, such asby washing with ammoniated water at a pH of about 9.0.

After washing, the solids are dried, as shown by drying step 60. Theresulting product is a niobium pentoxide hydrate powder having a narrowparticle size distribution and a desired particle size. Calcination ofthe niobium pentoxide hydrate converts it to niobium pentoxide, Nb₂O₅.

It should be noted that although the foregoing description describes apreferred process for producing a niobium pentoxide product, a similarprocess may be utilized for producing other valve metal pentoxideproducts, such as tantalum pentoxide products. Moreover, although theaddition of materials and reagents has been described with reference toparticular portions of the reaction vessels, the materials and reagentsmay be added to alternative portions of the reaction vessels in order toproduce pentoxide products with different characteristics. For example,in the first reaction vessel, the niobium containing fraction 2, may beadded to the inner periphery of the vessel and the ammonia solutionadded to the outer periphery of the vessel. It should further beunderstood that although the foregoing embodiment utilizes threereaction vessels, the process of the present invention may be conductedutilizing a fewer number or greater number of reaction vessels,depending on the characteristics desired in the final product. Althoughthe foregoing embodiment of the reaction utilizes the mixing and flowsas shown, reverse flows may be used as well. Furthermore, a portion ofthe solids discharged from the third reactor may be recycled to coarsenand densify the particles as desired.

The present invention also provides new valve-metal pentoxide powders:

A first embodiment of calcined niobium pentoxide powders of the presentinvention may be characterized by having:

-   -   a BET surface area ≦6 m²/g, preferably ≦3 m²/g, more preferably        ≦1 m²/g; and    -   a packed bulk density of >1.8 g/cc, preferably ≧2.1 g/cc.        The first embodiment of calcined niobitum pentoxide powders may        be further characterized as comprising substantially spherical        particles.

A second embodiment of calcined niobium pentoxide powders of the presentinvention may be characterized by having:

-   -   a BET surface area of ≧2 m²/g, preferably ≧4 m²/g, more        preferably ≧6 m²/g; and    -   a packed bulk density of ≦1.8 g/cc, preferably ≦1.0 g/cc, more        preferably ≦0.75 g/cc.

A first embodiment of calcined tantalum pentoxide powders of the presentinvention may be characterized by having:

-   -   a BET surface area of ≦3 m²/g, preferably ≦0.75 m²/g, more        preferably ≦0.4 m²/g; and    -   a packed bulk density of >3.0 g/cc, preferably ≧3.8 g/cc, more        preferably ≧4.0 g/cc.        The first embodiment of calcined tantalum pentoxide powders may        be further characterized as comprising substantially spherical        particles.

A second embodiment of calcined tantalum pentoxide powders of thepresent invention may be characterized by having:

-   -   a BET surface area of ≧3 m²/g, preferably ≧7 m²/g; more        preferably ≧11 m²/g, and    -   a packed bulk density of ≦3.0 g/cc, preferably ≦1.1 g/cc, more        preferably ≦0.75 g/cc.

The first and second embodiments of niobium pentoxide products of thepresent invention may be generally characterized by the followingcombination of analytical properties: Size: 70% less than 1 micrometerto <1% less than 1 micrometer Morphology: fine single crystallites tocoarse substantially spherical agglomerates BET Surface Area: 0.50 m²/gto 50 m²/g -- uncalcined 0.50 m²/g to 6 m²/g -- calcined Packed BulkDensity: 0.5 g/cc to 2.1 g/cc;

wherein the first embodiment of niobium pentoxide products is furthercharacterized by having Size: <1% less than 1 micrometer Morphology:large substantially spherical agglomerates BET Surface Area: 0.5 m²/g to3 m²/g -- uncalcined 0.5 m²/g to 2 m²/g -- calcined Calcined Packed BulkDensity: 1.8 g/cc to 2.1 g/cc;

and wherein the second embodiment of niobium pentoxide products isfurther characterized by having Size: 70% less than 1 micrometerMorphology: fine crystallites BET Surface Area: 3 m²/g to 50 m²/g --uncalcined 2 m²/g to 6 m²/g -- calcined Packed Bulk Density: 1.0 g/cc to1.8 g/cc.

The first and second embodiments of tantalum pentoxide products of thepresent invention may be generally characterized by the followingcombination of analytical properties: Size: 70% less than 1 micrometerto <1% less than 1 micrometers Morphology: fine single crystallites tolarge substantially spherical agglomerates BET Surface Area: 0.3 m²/g to17 m²/g -- uncalcined 0.3 m²/g to 11 m²/g -- calcined Calcined PackedBulk Density: 0.9 to 4.0 g/cc

wherein the first embodiment of tantalum pentoxide products is furthercharacterized by having Size: substantially all >1 micrometerMorphology: large substantially spherical agglomerates BET Surface Area:0.3 m²/g to 3 m²/g -- uncalcined 0.3 m²/g to 3 m²/g -- calcined CalcinedPacked Bulk Density: 2 g/cc to 4 g/cc;

and wherein the second embodiment of tantalum pentoxide products isfurther characterized by having Size: >9% less than 1 micrometerMorphology: fine crystallites BET Surface Area: 3 m²/g to 17 m²/g --uncalcined 1.8 m²/g to 11 m²/g -- calcined Calcined Packed Bulk Density:1.1 g/cc to 3.0 g/cc.

The products of the present invention may be advantageously produced,for example, by the process of the present invention.

An advantage of the products of the present invention is that theproducts of high purity can be obtained. The fine particles produced bythe present invention are highly reactive for use as dopants in variousapplications, such as electronics, ceramics, and as catalysts. The largedense spherical agglomerated particles have exceptional rheology and canbe used for thermite (thermal reduction processes with active metals,i.e., aluminum) or glass applications. The large spherical particlesblend well upon mixing with other glass forming ingredients.Furthermore, the large dense particles are not readily airborne in highgas flow streams, thus resulting in high melt efficiencies. Otherapplications for thermiting, for example, result in the large densespherical particles giving greater packing factors, thus large thermitebatches and greater productivity. In addition, the large, denseparticles are not readily airborne during the thermite reaction, thusresulting in greater product recoveries.

In addition, the present invention provides new valve metal pentoxideprecursors, in particular new niobium pentoxide precursors and newtantalum pentoxide precursors. The valve metal pentoxide precursors ofthe present invention may be processed to produce advantageous valvemetal pentoxide products.

The valve metal pentoxide precursors of the present invention arecharacterized by having a line broadened d-value under x-ray analysisat:

-   -   6±0.3;    -   3±0.2; and    -   1.8±0.1.        FIG. 7 is an example of the type of line broadened d-value graph        which may be generated by a valve metal pentoxide precursor of        the present invention under x-ray analysis. FIG. 7 is provided        by way of example only and should not be construed as limiting        the scope of the valve metal pentoxide precursors of the present        invention.

A first embodiment of niobium pentoxide precursors of the presentinvention may be further characterized by having a BET surface area of≦3 m²/g, preferably ≦0.5 m²/g and a Fluoride content of ≦500 parts permillion (ppm), preferably ≦150 ppm.

A second embodiment of niobium pentoxide precursors of the presentinvention may be further characterized by having a BET surface areaof >3 m²/g, preferably ≧50 m²/g and a Fluoride content of ≦500 ppm,preferably ≦150 ppm.

A first embodiment of tantalum pentoxide precursors of the presentinvention may be further characterized by having a BET surface area of≦3 m²/g, preferably ≦0.4 m²/g and a Fluoride content of ≦500 ppm,preferably ≦150 ppm.

A second embodiment of tantalum pentoxide precursors of the presentinvention may be further characterized by having a BET surface areaof >3 m²/g, preferably ≧17 m²/g and a Fluoride content of ≦500 ppm,preferably ≦150 ppm.

The valve-metal pentoxide precursors of the present invention may beadvantageously produced by the process of the present invention byseparating the valve-metal pentoxide precursor prior to converting theprecursor to a valve-metal pentoxide.

The following analytical procedures may be utilized in determining theanalytical properties of the products of the present invention, and/orwere utilized in the examples described herein.

B.E.T. Surface Area

B.E.T. surface area was determined according to Cabot test procedureWI-P008, revision number 3 (5/1995) by measuring the quantity ofadsorbate gas adsorbed in a solid surface by sensing the changing inthermal conductivity of a flowing mixture of adsorbate and inert carriergas utilizing a monosorb surface area analyzer Model No. MS-12 and aquantector outgassing unit. The procedure included the following:

-   -   i) purging the gas cylinders for at least 5 minutes;    -   ii) purging the instrument for 5 minutes;    -   iii) adjusting gas flow pressure to position the float between        60 and 80;    -   iv) warming up the instruments for 20-30 minutes;    -   v) resetting the counter;    -   vi) calibrating the instruments by injecting 1.0 cc. of air into        the septum on the front panel using the syringe. (The counter        should begin operating in about 2 minutes. The air injection        should yield a reading of 2.84±0.03. If the reading is greater        than 2.87, increase the gas flow slightly. If the reading is        less than 2.81, decrease the gas flow slightly.)    -   vii) verifying the calibration;    -   viii) weighing a sample to the nearest 0.0001 grams;    -   ix) placing the sample in a sample tube;    -   x) inserting the sample tube into a tube holder and inserting        the tube holder into the outgas station;    -   xi) placing the heating mantle (150° C.) around the sample tube;    -   xii) collecting outgas sample for at least 20 minutes;    -   xiii) removing the sample tube and tube holder from the sample        station;    -   xiv) removing the outgas sample from the outgas station;    -   xv) inserting the outgassed sample into the sample station;    -   xvi) depressing the “ADS” button under the signal meter;    -   xvii) zeroing the signal meter;    -   xviii) jacketing the outgassed sample tube with a Dewar flask        80-90% filled with liquid nitrogen;    -   xix) depressing the “DES” button after the signal meter returns        to zero    -   xx) removing the Dewar flask and immediately immersing the        sample in a beaker of room temperature (approximately 20° C.)        water, (After approximately 1 minute, the desorption is        complete, the signal meter will return to zero, and the counter        will display a number which is the sample surface area in square        meters.) and recording the displayed number;    -   xxi) removing and drying the sample tube; and    -   xxii) weighing the sample tube.        B.E.T. surface area is determined by the following calculations:        surface area m²/g=Counts/(Total weight−Tare weight).        A control powder of known B.E.T. surface area is run to verify        the accuracy of the procedure.        Flouride Content (Greater than or Equal to 50 ppm)

For samples having a fluoride content of greater than 50 ppm, fluoridecontent was determined utilizing Cabot Test Procedure W-108“Determination of Fluoride in Tantalum Wet Method,” revision number 1(10/1992). The method provides for the determination of fluoride intantalum in the range of 0.005 to 0.50 percent. Following alkalinefusion, fluoride is separated by volatilization as silicon tetrafluoridefrom a sulfuric acid solution. Fluoride content is determined in thedistillate using a specific ion electrode. The procedure includes thefollowing steps:

-   -   i) Transfering 1.000 grams of sample to a 100 ml nickel        crucible.    -   ii) Adding 5.0 grams of KOH and mix.    -   iii) Covering and heating under low heat until the sample has        completely turned milky white.    -   iv) Cooling and leaching the melt with 25 ml of deionized water.    -   v) Transfering the sample to the distillation flask containing a        few glass beads.    -   vi) Placing a 600 ml beaker containing 30 ml of water, 5 drops        of Bromothymol blue indicator and 3 ml of 30% sodium hydroxide        under the condenser so that the condenser tip is immersed in the        sodium hydroxide solution.    -   vii) Adding 80 ml of 1:1 sulfuric acid through the funnel and        close the stopcock.    -   viii) Using a burner, gradually raising the temperature in the        distillation flask to 140° C. and maintain this temperature        within ±5° C. while passing steam from a steam generation flask        containing DI water.    -   ix) Collecting about 400 ml of distillate and transfer to a 500        ml volumetric flask.    -   x) Diluting to 500 ml with DI water and mix.    -   xi) Transfering an aliquot containing between 5 and 50 μg of        fluoride to a 150 ml beaker. Diluting to 50 ml with DI water and        add 50 ml of buffer solution.    -   xii) Placing on a magnetic stirrer and mix at medium speed.    -   xiii) Immersing the electrodes in the solution for at least        three minutes or until the reading has stabilized.    -   xiv) Recording the reading and calculating the μg of fluoride        from the calibration curve.    -   xv) Calibration Curve:        -   Preparing a calibration curve by diluting the fluoride            standard solution to the appropriate volumes to make 0.1 μg,            0.25 μg, 0.5 μg, and 1.0 μg/ml standards.            Flouride content is determined by the following calculation:            (μg/ml×500 ml)/(Sample Weight in Grams)=ppm flouride.            A control sample of known flouride content is run to verify            the accuracy of the procedure.            Flouride Content (Less than or Equal to 50 ppm)

For samples having a fluoride concentration less than or equal to 50parts per million, fluoride content was determined according to CabotTest Method W-80 “Determination of Fluorine by Thorium Nitrate TitrationWet Method,” revision number 2 (2/1993). In this method, fluorine isseparated by volatilization as tetrafluorides from a sulfuric acidsolution. The aqueous solution is titrated with the standard solution ofthorium nitrate using alizarin sulfonate as an indicator in order todetermine fluoride content. The procedure includes the following steps:

-   -   i) Taking appropriate sample weight or aliquot and transfer to        an all glass distillation flask containing a few glass beads.    -   ii) Placing a 600 ml. beaker containing 30 ml. of water, 5 drops        of Brom Thymol Blue indicator and 5.0 ml. of 30% sodium        hydroxide under the condenser so that the condenser tip is        immersed in the sodium hydroxide solution. (If necessary, add        more NaOH to maintain blue color during the distillation.)    -   iii) Adding 80.1 ml. of 1:1 sulfuric acid through the funnel and        close the stopcock.    -   iv) Using a burner, gradually raising the temperature in the        distillation flask to 145° C. and maintaining this temperature        within 5° while passing in steam from a steam generation flask        containing distilled water.    -   v) Collecting about 400 ml. of distillate and transfer to a        500 ml. volumetric flask.    -   vi) Diluting to 500 ml. with water and transfering an aliquot        containing 5 to 10 mg. of fluoride to a 150 ml white casserole.    -   vii) Adding 5 drops of indicator and then 5% acetic until the        pink color is just discharged.    -   viii) Adding 3 ml. of buffer solution and titrating with thorium        nitrate to a permanent pink color. (In order to get acquainted        with the end point, it is good practice for the operator to        titrate various amounts of fluorine made from a standard sodium        fluoride solution containing 0.500 mg. fluoride/ml. The        illumination should be the same for all titrations subsequent to        the standardization.)        Flouride content is determined by running a blank and a flouride        standard containing 5 mg of fluoride as outlined in steps (vi)        to (viii), and then utilizing the following calculations:        ${{mg}\quad F\quad{sample}} = \frac{\begin{matrix}        {\left( {{mg}\quad F\quad{standard}} \right) \times} \\        \left( {{{sample}\quad{titration}} - {{blank}\quad{titration}}} \right)        \end{matrix}}{\left( {{{sample}\quad{titration}} - {{blank}\quad{titration}}} \right)}$        ${g\text{/}l\quad{Flouride}} = {\frac{{mg}\quad{fluoride}\quad{sample}}{\begin{matrix}        {(10) \times \left( {10/100} \right) \times {aliquot}\quad{from}} \\        {{step}\quad({vi})\quad{of}\quad{the}\quad{procedure}}        \end{matrix}}.}$        A control sample of known flouride content is run to verify the        accuracy of the procedure.        Particle Size

Particle size was determined according to Cabot Test Procedure P-007“Determination of Particle Size With a Micro-Trac II Physical Method,”revision number 2 (11/1994). This procedure provides for thedetermination of particle size of powders using the principle of lightscattering with a laser beam source in the range of 0.7 to 700 microns.The procedure includes the following steps:

-   -   i) Turning on the power to the computer, monitor and printer.    -   ii) Turning on the power to the Micro-Trac II unit.    -   iii) Draining and rinsing the re-circulator attached to the        Micro-Trac II unit. Fill to 1/2 inch above the top of the return        tube located inside the sample chamber using deionized water,        approximately 240 ml.    -   iv) Turning the re-circulator switch on and off a few times to        purge any air bubbles from the lines. Watching for a large        bubble to rise from the small cavity at the bottom of the sample        chamber.    -   v) Allowing the water to circulate for approximately one minute        to remove entrained bubbles.        -   NOTE: Turning the switch on and off a few times helps remove            the bubbles.    -   vi) From the computer menu, choosing Data Management System and        press Enter and the F2 key for Data Collection.    -   vii) Pressing F9. This will cause primary keypad to be        displayed. “Laser Align” will be highlighted. Aligning the        laser, if necessary, by following the procedure outlined in the        Micro-Trac Operators Manual.    -   viii) Selecting “Run Time” from the menu of the primary keypad.        Setting run time to 30 seconds.    -   ix) Selecting “Set Zero” from keypad. Press Enter. Numbers will        appear in two columns, Flux and Normalized Flux. Numbers should        be progressively lower down both columns.        -   NOTE: If high background warning appears, try turning            re-circulator switch on and off a few times.    -   x) When satisfactory numbers are obtained in step (ix),        re-selecting “Run Time” from the keypad menu and resetting run        time to 10 seconds.    -   xi) From the primary keypad screen, selecting F1 to return to        DMS. Channel screen will appear.    -   xii) Pressing Ctrl and F3 simultaneously to obtain a blank run.        Numbers should all be zeros. If all zeros do not appear,        repeating steps (vii) through (xii) until all zeros from the        blank run.    -   xiii) Pressing F9 to return to primary keypad.    -   xiv) Moving highlighter to Sample Loading and press Enter.    -   xv) Pressing F1 for Sample Loading.    -   xvi) Introducing sample slowly until loading index reads        0.86-0.90. Waiting 15 to 30 seconds to see that reading is        stable.    -   xvii) Pressing Esc F1 which will return you to the channel        screen. Pressing Control and F3 together to make sample run.    -   xviii) Checking upper channels to see that there are no false        readings (i.e., no zeros between real numbers or readings in        highest channels when majority of reading indicate a fine        powder.    -   xix) If false reading occurs, repeating the prior two steps. If        false readings appear a second time, dump sample and restart        from step (vii).    -   xx) Moving cursor down to Sample ID and entering sample        information.    -   xxi) Pressing F5 to save the results to the hard disk.    -   xxii) Pressing Print Screen to print a hard copy of the results.    -   xxiii) Opening drain valve, and shutting off re-circulator        before chamber empties.    -   xiv) Rinsing 2-3 times with re-circulator running.    -   xv) Draining and refilling with deionized water.    -   xvi) Pressing F9 and proceeding from step (ix) for next sample        to be analyzed.        A control powder, of known particle size distribution, is run to        verify the accuracy of the procedure.        Bulk Density and Tap (Packed Bulk) Density

Bulk density and tap density (packed bulk density) were determined byweighing samples of the powders and measuring the volume of the samplesbefore and after tapping. The tapping machine utilized was manufacturedby German J. Engelsmann. The procedure included the following steps:

-   -   i) Taring a 25 ml glass graduated cylinder.    -   ii) Transfering, carefully, between 20 and 25 ml of the material        to be tested to the graduate.    -   iii) Recording the weight of the sample.    -   iv) Recording the volume of the sample taking care not to pack        down the sample.    -   v) Placing the cylinder under the ring of the tapping machine        and secure it.    -   vi) Turning the switch of the instrument “ON.” It will tap 5,000        times and shut off automatically.    -   vii) Removing the graduated cylinder and remeasuring the volume.        Bulk density was calculated by the following formula:        Bulk Density=Weight in Grams/Original Volume        A control sample of known bulk density is run to verify the        accuracy of the procedure.        X-Ray Defraction (XRD)

X-ray defraction (XRD) data was produced utilizing procedures developedby Micron Inc., 3815 Lancaster Pike, Wilmington, Del. The data wasproduced utilizing a General Electric XRD-5 defractometer with a coppertarget tube and graphite monochromator, a scintillation detector withpulse height selection and a computer controlled step-scanning drive.The x-ray defraction system also included the following computerhardware and computer software:

-   -   Digital Micro VAX-2000    -   Falcon microprocessor for step-scanning control    -   HP 7475A 6-color plotter for hard copy of scans    -   Toshiba P321 printer for hard copy of print-outs    -   Tektronix color graphics terminal    -   Nicolet/Siemens I2 Polycrystalline Software Package (Version        2.41 June 1989). This software package uses the VMS operating        system. The menu-driven program is for data collection,        peak-picking (data reduction), search/match phase identification        using the JCPDS data base, quantitative analysis and interactive        graphics.

The data collection reduction and reporting procedures were as follows:

Data Collection Procedure:

Clean the goniometer sample holder prior to inserting the standard.Insert the standard into the sample holder and align the sample faceparallel to the sample holder face. Small displacement of the sampleface with respect to the sample holder face will cause the diffractionspectra to shift with respect to the theoretical 2 theta values. Run thediffraction scan of the Silicon standard using the parameters listedunder “Instrument Operating Conditions” on page 1.

Data Reduction Procedures:

Measure the 2 theta values and intensities of the peaks at 28.443degrees and at 88.032 degrees.

Data Reporting:

Record the measured values in the XRD calibration log. If the measured 2theta values deviate more than 0.04 degrees 2 theta from the theoreticalvalues or the intensities deviate more than 20% relative to the previousestablished values the laboratory supervisor must be advised andappropriate measures taken to correct the problem. An “Out ofSpecification” form must be made out, following the procedure outlinedin SOPOOS. Samples that were analyzed during the discrepancy must bere-analyzed after the discrepancy has been corrected.

Morphology

Morphology of the samples may be determined by visual inspectionutilizing scanning electron microscope photographs as necessary.

Other properties may be determined by procedures which, like theforegoing procedures, are well known and generally utilized in the art.

The effectiveness and advantages of various aspects and embodiments ofthe present invention will be further illustrated by the followingexamples.

EXAMPLES

General Description of Reaction Set-Up

The following set-up was utilized in Examples 1-10.

Three reaction vessels with accompanying hardware were utilized. Thereactor train design and layout was substantially as depicted in FIG. 1.

Three 1500 ml (milliliter) plastic beakers were utilized as the first,second, and third reaction vessel. Working volume of the reactors wasapproximately 1000 ml. The plastic beakers were heated by hotplates in adouble boiler type set-up using an outer container surrounding eachbeaker. Either water or Dowtherm®, a registered heat exchange product ofDow Chemical Co., was utilized in the outer containers for heat transferand control depending on temperature requirements. In order to obtain adraft tube set-up, an inner tube with flights (or baffles) was utilizedinside each beaker.

Variable speed marine propellers were utilized in the bottom of eachbeaker as circulation means and variable speed peristaltic pumps wereutilized to control the feed rates of the niobium fraction and ammoniasolution to the first two beakers (reactors).

Example 1

This example illustrates a laboratory scale embodiment of a preferredprocess of the present invention for making niobium pentoxide precursor,and a niobium pentoxide (Nb₂O₅) product of the present invention.

Reactor bath double boilers (filled with deionized (DI) water) were setto 98° C. A stock solution of niobium oxyfluoride (concentration of 210g niobium pentoxide/liter) was preheated to about 76° C. and added toreactor one at an average rate of 18.5 ml/minute. Stock solution of 5N(7.8 wt. %) ammonia was added to reactor one at an average rate of 80.5ml/minute. The reactants were agitated in the first reactor with aresultant average temperature and pH of 74° C. and 8.52, respectively.The resulting suspension flowed into the second and third reactors forfurther mixing. The reaction was run for 330 minutes, prior tocollection of samples, for a total of approximately ten residence times,average residence time being 31 minutes.

Two liters of suspension were collected and filtered. The retained cakewas washed and re-slurried with two liters of 5N ammonia solution atabout 80° C. The resulting slurry was then filtered. The wash andfiltration were repeated four more times. The resulting retained cakewas dried for sixteen hours at 85° C.

The dried cake was then calcined at 900° C. for four hours. Theuncalcined cake weighed 187 g (28.4% moisture) and contained 200 ppmfluoride. The calcined cake weighed 97.5 g containing 100 ppm fluorideand 90.9% of the material was below 1.5 microns in size (100% was below24 microns).

The process conditions utilized and results obtained are also set forthin Table 1 below.

Example 2

This example illustrates a laboratory scale embodiment of a preferredprocess of the present invention for making niobium pentoxide precursorand a niobium pentoxide (Nb₂O₅) product of the present invention.

Reactor bath double boilers (filled with DI water) were set to 98° C.Stock solution of niobium oxyfluoride (concentration of 210 g niobiumpentoxide/liter) was preheated to about 76° C. The niobium solution wasadded to the first reactor at an average rate of 13.1 ml/minute. Stocksolution of 5N (7.8 wt. %) ammonia was also added to reactor one at anaverage rate of 98.2 ml/minute. These reactants were then agitated witha resultant average temperature and pH of 61° C. and 9.14, respectively.

The resulting suspension flowed into the second reactor where anadditional 5.6 ml/minute of niobium oxyfluoride solution was added withagitation. The resultant average temperature and pH of reactor two were73° C. and 8.28, respectively. The resulting suspension flowed into thethird reactor for further mixing. The reaction was run for 315 minutes,prior to collection of samples, for a total of approximately elevenresidence times, average residence time being 27 minutes.

Two liters of suspension were collected and filtered. The filtered cakewas washed and re-slurried with two liters of 5N (7.8 wt. %) ammoniasolution at about 85° C. The resulting slurry was then filtered. Thewash and filtration were repeated four additional times. The resultingretained cake was dried for sixteen hours at 85° C. The dried cake wasthen calcined at 900° C. for four hours. The uncalcined cake weighed223.5 g (44.3% moisture) and contained 460 ppm fluoride. The calcinedcake weighed 85.8 g, containing 180 ppm fluoride and 73.5% of thematerial was larger than 96 microns in size.

The process conditions utilized and results obtained are also set forthin Table 1 below.

Example 3

This example illustrates a laboratory scale embodiment of a preferredprocess of the present invention for making niobium pentoxide precursorand a niobium pentoxide (Nb₂O₅) product of the present invention.

Reactor bath double boilers (filled with DI water) were set to 95° C. Astock solution of niobium oxyfluoride (concentration of 210 g niobiumpentoxide/liter) was preheated to about 88° C. and added to reactor oneat an average rate of 3.5 ml/minute. Stock solution of 5N (7.8 wt. %)ammonia was added to the first reactor at an average rate of 7.8ml/minute. These reactants were agitated with a resultant averagetemperature and pH of 76° C. and 7.78, respectively. The resultingsuspension flowed into the second reactor where an additional 15.6ml/minute of ammonia stock solution was added with agitation. Theresultant average temperature and pH of the second reactor were 68° C.and 8.48, respectively.

The resulting suspension flowed into the third reactor for furthermixing. The reaction was run for 1100 minutes, prior to collection ofsamples, for a total of approximately ten residence times, averageresidence time being 115 minutes.

Two liters of suspension were collected and filtered. The filtered cakewas washed and re-slurried with two liters of 5N (7.8 wt. %) ammoniasolution at about 85° C. The resulting slurry was then filtered. Thewash and filtration were repeated four additional times. The retainedcake was then dried for sixteen hours at 85° C. The dried cake was thencalcined at 900° C. for four hours. The uncalcined cake weighed 143.1 g(29.07% moisture) and contained 1400 ppm fluorine. The calcined cakeweighed 71.5 g containing 200 ppm fluoride and 77.5% of the materialfell between 8 and 32 microns in size (5.6% was below 8 microns).

The process conditions utilized and results obtained are also set forthin Table 1 below.

Example 4

This example illustrates a laboratory scale embodiment of a preferredprocess of the present invention for making niobium pentoxide precursorand a niobium pentoxide (Nb₂O₅) product of the present invention.

Reactor bath double boilers (filled with DI water) were set to 98° C. Astock solution of niobium oxyfluoride (concentration of 210 gramsniobium pentoxide/liter) was preheated to about 72° C. and added toreactor one at an average rate of 19 ml/minute. Stock solution of 5N(7.8 wt. %) ammonia was also added to reactor one at an average rate of34.3 ml/minute. These reactants were then agitated with a resultantaverage temperature and pH of 80° C. and 6.28, respectively.

The resulting suspension flowed into the second reactor where anadditional 20.9 ml/minute of ammonia stock solution was added withagitation. The resultant average pH of reactor two was 8.46(temperatures for reactor two were not recorded). The resultingsuspension flowed into the third reactor for further mixing. Thereaction was run for 375 minutes, prior to collection of samples, for atotal of approximately nine residence times, average residence timebeing 42 minutes. Two liters of suspension were collected and filtered.The filtered cake was washed and re-slurried with two liters of 5N (7.8wt. %) ammonia solution at about 85° C. The resulting slurry was thenfiltered. The wash and filtration was repeated four additional times.The resulting retained cake was dried for twenty hours at 90° C. Thedried cake was then calcined at 900° C. for four hours. The uncalcinedcake weighed 216.6 grams (49.9% moisture) and contained 3600 ppmfluoride. The calcined cake weighed 82.2 grams containing 300 ppmfluoride and 30.5% of the material was smaller than 1 micron in size.

The process conditions utilized and results obtained are also set forthin Table 1 below.

Example 5

This example illustrates a laboratory scale embodiment of a preferredprocess of the present invention for making niobium pentoxide precursorand a niobium pentoxide (Nb₂O₅) product of the present invention.

Reactor bath double boilers (filled with DI water) were set to 98° C. Astock solution of niobium oxyfluoride (concentration of 210 gramsniobium pentoxide/liter) was preheated to about 75° C. and added toreactor one at an average rate of 56.5 ml/minute. Stock solution of 5N(7.8 wt. %) ammonia was also added to reactor one at an average rate of210.4 ml/minute. These reactants were then agitated with a resultantaverage temperature and pH of 80° C. and 7.72, respectively.

The resulting suspension flowed into the second reactor where additionalammonia stock solution 5N (7.8 wt. %) was added with agitation to raisethe pH of the resulting solution to 8.49 and the temperature to 70° C.The resulting suspension flowed into the third reactor for furthermixing. The reaction was with an average residence time of 12 minutes.

Two liters of suspension were collected and filtered. The filtered cakewas washed and re-slurried with two liters of 5N (7.8 wt %) ammoniasolution at about 85° C. The resulting slurry was then filtered. Thewash and filtration was repeated four additional times. The resultingretained cake was dried for 16 hours at 85° C. at 35.78% moisture. Thedried cake was then calcined at 900° C. for four hours. The calcinedcake contained 100 ppm fluoride with a packed bulk density of 1.02 g/ccand 28.4% was less than 1 micron in size.

The process conditions utilized and results obtained are also set forthin Table 1 below.

Example 6

This example illustrates a laboratory scale embodiment of a preferredprocess of the present invention for making tantalum pentoxide precursorand a tantalum pentoxide (Ta₂O₅) product of the present invention.

Reactor bath double boilers (filled with DOW thermal oil) were set to160° C. Stock solution of fluorotantalic acid (concentration of 80 gtantalum pentoxide/liter) was preheated to about 67° C. and added toreactor one at an average rate of 30 ml/minute. Stock solution of 5N(7.8 wt. %) ammonia was added to the first reactor at an average rate of50 ml/minute. The reactants were agitated with a resultant averagetemperature and pH of 67° C. and 9.01, respectively.

The resulting suspension flowed into the second reactor for furtheragitation with a resultant average temperature and pH of 72° C. and8.73, respectively. The suspension flowed into the third reactor forfurther agitation with a resultant average temperature and pH of 78° C.and 8.42, respectively. The reaction was run for 180 minutes, prior tocollection of samples, for a total of about five residence times,average residence time being 37.5 minutes.

Three liters of suspension were collected and filtered. The filteredcake was washed and re-slurried with two liters of 5N (7.8 wt. %)ammonia solution at about 85° C. The resulting slurry was then filtered.The wash and filtration were repeated four additional times. Theretained cake was dried for six hours at 100° C. The dried cake was thencalcined at 900° C. for one hour. The uncalcined cake weighed 121.7 g(2.43% moisture) and contained 50 ppm fluoride. The calcined cakeweighed 108 g containing less than 50 ppm fluoride and 78.6% of thematerial was smaller than 1 micron in size.

The process conditions utilized and results obtained are also set forthin Table 1 below.

Example 7

This example illustrates a laboratory scale embodiment of a preferredprocess of the present invention for making tantalum pentoxide precursorand a tantalum pentoxide (Ta₂O₅) product of the present invention.

Reactor bath double boilers (filled with DOW thermal oil) were set to180° C. Stock solution of fluorotantalic acid (concentration of 80 gtantalum pentoxide/liter) was preheated to about 66° C. and added toreactor one at an average rate of 30 ml/minute. A stock solution of 5N(7.8 wt. %) ammonia was added to the first reactor at an average rate of35 ml/minute. The reactants were agitated with a resultant averagetemperature and pH of 74° C. and 8.42, respectively.

The resulting suspension flowed into the second reactor for furtheragitation with a resultant average temperature and pH of 77° C. and8.20, respectively. The suspension then flowed into the third reactorfor further agitation with a resultant average temperature and pH of 82°C. and 7.97, respectively. The reaction was run for 255 minutes, priorto collection of samples, for a total of about six residence times,average residence time being 46 minutes.

Four liters of suspension were collected and filtered. The filtered cakewas washed and re-slurried with two liters of 5N (7.8 wt. %) ammoniasolution at about 85° C. The resulting slurry was then filtered. Thewash and filtration were repeated four additional times. The resultingretained cake was dried for six hours at 100° C. The dried cake was thencalcined at 900° C. for one hour. The uncalcined cake weighed 231.8 g(1.35% moisture) containing 310 ppm fluoride and 95.8% of the materialwas smaller than 8 microns in size.

The process conditions utilized and results obtained are also set forthin Table 1 below.

Example 8

This example illustrates a laboratory scale embodiment of a preferredprocess of the present invention for making tantalum pentoxide precursorand a tantalum pentoxide (Ta₂O₅) product of the present invention.

Reactor bath double boilers (filled with DOW thermal oil) were set to190° C. Stock solution of fluorotantalic acid (concentration of 80 gtantalum pentoxide/liter) was preheated to about 73° C. and added toreactor one at an average rate of 25 ml/minute. A stock solution of 5N(7.8 wt. %) ammonia was added to the first reactor at an average rate of18 ml/minute. The reactants were agitated with a resultant averagetemperature and pH of 83° C. and 7.53, respectively.

The resulting suspension flowed into the second reactor where anadditional 50 ml/minute of ammonia stock solution was added withagitation. The resultant average temperature and pH in the secondreactor were 60° C. and 9.50, respectively. The resulting suspensionthen flowed into the third reactor for further mixing with a resultantaverage temperature and pH of 71° C. and 9.08, respectively. Thereaction was run for 255 minutes, prior to collection of samples, for atotal of approximately eight residence times, average residence timebeing 33 minutes.

Six liters of suspension were collected and filtered. The filtered cakewas washed and re-slurried with two liters of 5N (7.8 wt. %) ammoniasolution at about 85° C. The resulting slurry was then filtered. Thewash and filtration were repeated four additional times. The retainedcake was dried for six hours at 100° C. The dried cake was then calcinedat 900° C. for one hour. The uncalcined cake weighed 128.9 g (4.07%moisture) and contained 50 ppm fluoride. The calcined cake weighed 107.2g containing less than 50 ppm fluoride and 71.9% of the material waswithin the size range of 8 to 32 microns.

The process conditions utilized and results obtained are also set forthin Table 1 below.

Example 9

This example illustrates a laboratory scale embodiment of a preferredprocess of the present invention for making tantalum pentoxide precursorand a tantalum pentoxide (Ta₂O₅) product of the present invention.

The reactor train design and layout was as depicted in FIG. 1. Theworking volume of the 3 reactors was 1000 ml per reactor. Dowtherm wasused for the heat exchange from the vessels to the 3 reactors. The useof variable speed agitators set at approximately 550 rpm was used in the3 reactors.

Stock solution of fluorotantalic acid (concentration of 87 g. tantalumpentoxide/liter) and 0.7% by volume EDTA was added to reactor 1 at aconstant rate. Stock solution of 30* ammonium hydroxide (NH₄OH) wasadded to the first reactor at an automated rate to achieve an average pHof 7.49. The average temperature of the reactants in reactor 1 was63.92° C. Stock solution of 30% ammonium hydroxide (NH₄OH) was thenadded to the second reactor at a constant rate with a resulting averagepH of 8.55 and temperature of 61.8° C. The resulting suspension in thesecond reactor then flowed into the third reactor for further agitationwith an average temperature and pH of 63.5° C. and 8.14 respectively.The reaction was run for 240 minutes prior to collection of samples, fora total of 4 residence times, average residence time being 120 minutes.The product from the collection vessel was then filtered, washed, andre-slurried in an ammonia solution 5 times. The retained cake was vacuumdried at 110° C. for 3 hours (10% moisture) and contained 90 ppmfluorides. The cake was then calcined at 1050° C. for 1 hour (14%moisture) and contained 70 ppm fluoride.

The process conditions utilized and results obtained are also set forthin Table 1 below.

Example 10

This example illustrates a laboratory scale embodiment of a preferredprocess of the present invention for making tantalum pentoxide precursorand a tantalum pentoxide (Ta₂O₅) product of the present invention.

The reactor train design and layout was as depicted in FIG. 1. Theworking volume of the 3 reactors was 1000 ml per reactor. Dowtherm wasused for the heat exchange from the vessels to the 3 reactors. The useof variable speed agitators set at approximately 550 rpm was used in the3 reactors.

Stock solution of fluorotantalic acid (concentration of 87 g. tantalumpentoxide/liter) and 0.7% by volume EDTA was added to reactor 1 at aconstant rate. Stock solution of 30% ammonium hydroxide (NHOH) was addedto the first reactor at an automated rate to achieve an average pH of9.51. The average temperature of the reactants in reactor 1 was 55.6° C.Stock solution of 30% ammonium hydroxide (NH₄OH) was then added to thesecond reactor at a constant rate with a resulting average pH of 9.06and temperature of 53.3° C. The resulting suspension in the secondreactor then flowed into third reactor for further agitation with anaverage temperature and pH of 55° C. and 8.84 respectively. The reactionwas run for 240 minutes prior to collection of samples, for a total of 4residence times, average residence time being 120 minutes. The productfrom the collection vessel was then filtered, washed, and re-slurried inan ammonia solution 5 times. The retained cake was vacuum dried at 110°C. for 3 hours (41% moisture) and contained 130 ppm fluorides. The cakewas then calcined at 900° C. for 1 hour (35% moisture) and contained 70ppm fluoride.

The process conditions utilized and results obtained are also set forthin Table 1 below. TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 Compound Nb₂0₅Nb₂0₅ Nb₂0₅ Nb₂0₅ Nb₂0₅ Ta₂0₅ Ta₂0₅ Ta₂0₅ Ta₂0₅ Ta₂0₅ pH Rx. 1 8.52 9.147.78 6.28 7.72 9.01 8.42 7.53 7.5 9.51 pH Rx. 2 8.39 8.28 8.48 8.46 8.498.73 8.2 9.5 8.5 9.06 Total Residence 31 27 115 42 12 38 4.6 33 120 120Time (Min.) Temp. ° C. 74 61 76 80 80 67 74 83 64 56 Rx 1 Rx. Split100:0.0 70:30 33:67 62:38 76:67 100:0 100:0 26:74 52:48 100:0 Rx. 1%:Rx.2% Filtered F (ppm) 21500 80000 64000 135000 13500 54000 75000 750032000 96000 Uncalcined Washed F (ppm) 260 460 1400 3600 2350 50 310 <5090 130 Calcined F (ppm) 100 100 200 300 100 <50 200 80 120 70 SettledVol. ml. 240 270 20 320 90 155 120 15 30 176 Freefall Density g/cc 1.241.57 1.51 1.23 0.74 1.36 1.32 2.35 2.65 0.98 Packed Density g/cc 1.711.84 2.06 1.62 1.02 1.81 1.77 2.96 3.98 1.60 Uncalcined Percent 28.444.3 29.1 49.9 35.8 11.3 11.9 16.3 10 35 Moisture % < 1 μm 70.3 15.3 1.430.5 28.4 78.6 10.6 5.8 0 2.7 90%, < μm size 1.5 150 27 96 20 5 5 55 353.5 Surface Area m²/g 2.82 — 0.5 2.18 — 6.7 — 4.96 1.01 5.17Rx. 1 = Reaction in first reaction vesselRx. 2 = Reaction in second reaction vessel% < 1 μm = percentage of product smaller than 1 micrometer90% < μm = the particle size where 90% of particles are less than orequal to the size

The results set forth in Table 1 indicate that a preferred process ofthe present invention may be utilized to produce a wide variety ofniobium pentoxide precursors, niobium pentoxide (Nb₂O₅) products,tantalum pentoxide precursors and tantalum pentoxide (Ta₂O₅) productswhich fall within the scope of the present invention.

These results also illustrate that the rate of precipitation andresidence time in the reactors for particle ripening can increaseproduct density. Scanning electron photomicrographs of materialprecipitated near the isoelectric point of 7.7 for Nb₂O₅ with a 115minute and a 12 minute residence time are shown in FIGS. 2 and 3,respectively. FIGS. 2 a, 2 b, 2 c and 2 d are scanning electronphotomicrographs of the Nb₂O₅ produced in Example 3, at differentmagnifications. FIGS. 3 a, 3 b, 3 c and 3 d are scanning electronphotomicrographs of the Nb₂O₅ produced in Example 5, at differentmagnifications. FIGS. 4 a, 4 b, 4 c and 4 d are scanning electronphotomicrographs of the Ta₂O₅ produced in Example 9, at differentmagnifications. FIGS. 5 a, 5 b, 5 c and 5 d are scanning electronphotomicrographs of the Ta₂O₅ produced in Example 10, at differentmagnifications.

As shown in FIGS. 2 a-2 d and 3 a-3 d, the low density particlesproduced and the 12 minute residence time and calcined (FIGS. 3 a-3 d)are very obvious versus the much denser particles of material producedwith a 115 minute residence time (FIGS. 2 a-2 d). Furthermore, becausethe crystallites are very closely packed, crystal intergrowth anddensification has been further assisted as can be seen in thephotomicrographs.

FIGS. 5 a-5 d show the fine calcined particles of Ta₂O₅ produced at pH9.5 with a 2 hour residence time. FIGS. 4 a-4 d show similar denseparticles of Ta₂O₅ produced at a pH of 7.5 and a 120 minute residencetime.

These photomicrographs FIGS. 2 a-d, 3 a-d, 4 a-d and 5 a-d exemplify arange of particles which can be produced utilizing the technology of thepresent invention.

The examples discussed herein further illustrate that the products ofthe present invention are ammonium fluoride and a microcrystalline valvemetal pentoxide hydrates with a readily defined line broadened x-raydiffraction pattern and the calcined pentoxide analog.

The Zeta potential of the pentoxide hydrate in the presence of ammoniumfluoride is negative at pH's of 8 or greater and positive at pH's of 6or less as shown by FIG. 6. The isoelectric point or point of zerocharge is in the range of pH 7-8. Precipitation at the isoelectric pointallows agglomeration and formation of dense substantially sphericalparticles. This feature of the process of the present invention allowsthe control of precipitated particle sizes. At pH's above and below theisoelectric point, the charged particles repel one another preventingagglomeration and fine particles are precipitated.

It should be clearly understood that the forms of the present inventionherein described are illustrative only and are not intended to limit thescope of the invention.

1. A process for producing a valve metal pentoxide comprising: reactingan aqueous fluoro-solution comprising a valve metal-fluoro compound withan ammonia containing solution under controlled temperature, pH andresidence time conditions to precipitate valve metal pentoxideprecursor; converting the valve metal pentoxide precursor to valve metalpentoxide; and separating and recovering the valve metal pentoxide.2-13. (canceled)
 14. A calcined niobium pentoxide powder characterizedby having: a BET surface area less than or equal to 3 m²/g; and a packedbulk density of greater than 1.8 g/cc.
 15. The calcined niobiumpentoxide powder of claim 14, wherein the BET surface area is less than,or equal to, 1 m²/g.
 16. The calcined niobium pentoxide powder of claim14, wherein the packed bulk density is greater than or equal to 2.1g/cc.
 17. A calcined niobium pentoxide powder characterized by having: aBET surface area of greater than or equal to 2 m²/g; and a packed bulkdensity of less than or equal to 1.8 g/cc.
 18. The calcined niobiumpentoxide powder of claim 17, wherein the BET surface area is greaterthan or equal to 6 m²/g.
 19. The calcined niobium pentoxide powder ofclaim 17, wherein the packed bulk density is less than or equal to 1.0g/cc. 20-25. (canceled)
 26. A valve metal pentoxide precursorcharacterized by having a line broadened d-value under x-ray analysisat: 6±0.3; 3±0.2; and 1.8±0.1. 27-35. (canceled)
 36. The calcinedniobium pentoxide powder of claim 17, wherein the BET surface area isfrom 2 m²/g to 6 m²/g.
 37. The calcined niobium pentoxide powder ofclaim 17, wherein the BET surface area is from 2 m²/g to 4 m²/g.
 38. Thecalcined niobium pentoxide powder of claim 17, wherein the BET surfacearea is from 4 m²/g to 6 m²/g.
 39. The calcined niobium pentoxide powderof claim 17, wherein said packed bulk density is less than or equal to1.0 g/cc.
 40. The calcined niobium pentoxide powder of claim 17, whereinsaid packed bulk density is less than or equal to 0.75 g/cc.
 41. Thecalcined niobium pentoxide powder of claim 17, wherein said packed bulkdensity is from 1.0 g/cc to 0.75 g/cc.
 42. The calcined niobiumpentoxide powder of claim 14, wherein said BET surface area is less thanor equal to 0.5 m²/g.
 43. The calcined niobium pentoxide powder of claim14, wherein said powder is spherical particles.
 44. The calcined niobiumpentoxide powder of claim 14, wherein said powder has a fluoride contentof less than or equal to 500 ppm.
 45. The calcined niobium pentoxidepowder of claim 14, wherein said powder has a fluoride content of lessthan or equal to 150 ppm.
 46. The calcined niobium pentoxide powder ofclaim 17, wherein said powder has a fluoride content of less than orequal to 500 ppm.
 47. The calcined niobium pentoxide powder of claim 17,wherein said powder has a fluoride content of less than or equal to 150ppm.
 48. The calcined niobium pentoxide powder of claim 14, wherein saidcalcined niobium pentoxide powder has a size such that 70% or less ofsaid powder has a size less than 1 micrometer.
 49. The calcined niobiumpentoxide powder of claim 14, wherein said calcined niobium pentoxidepowder has a size such that less than 1% of said powder has a size lessthan 1 micrometer.
 50. The calcined niobium pentoxide powder of claim14, wherein said calcined niobium pentoxide powder comprises a finesingle crystallite shape.
 51. The calcined niobium pentoxide powder ofclaim 14, wherein said calcined niobium pentoxide powder comprisesspherical agglomerates.
 52. The calcined niobium pentoxide powder ofclaim 14, wherein 100% of the calcined niobium pentoxide powder is below24 microns in size.
 53. The calcined niobium pentoxide powder of claim14, wherein said calcined niobium pentoxide powder has a particle sizewherein the majority of the powder has a size larger than 96 microns insize.
 54. The calcined niobium pentoxide powder of claim 14, wherein amajority of the powder has a size between 8 and 32 microns in size. 55.The calcined niobium pentoxide powder of claim 14, wherein about 30% orless of the calcined niobium pentoxide powder has a particle size ofless than 1 micron.
 56. The calcined niobium pentoxide powder of claim14, wherein about 15% or less of the calcined niobium pentoxide powderhas a particle size of less than 1 micron.